Photoelectric conversion elements are used in various photosensors, copying machines, solar cells, and the like. These photoelectric conversion elements have adopted various systems to be put into use, such as elements utilizing metals, elements utilizing semiconductors, elements utilizing organic pigments or dyes, or combinations of these elements. In particular, solar cells that make use of non-exhaustive solar energy do not necessitate fuels, and full-fledged practicalization of solar cells as an inexhaustible clean energy is being highly expected. Among these, research and development of silicon-based solar cells have long been in progress. Many countries also support policy-wise considerations, and thus dissemination of silicon-based solar cells is still in progress. However, silicon is an inorganic material, and has limitations per se in terms of throughput and molecular modification.
Under such circumstances, research is being vigorously carried out on dye-sensitized solar cells. Especially, to have built momentum toward such research is research results by Graetzel et al. of École Polytechnique Fédérale de Lausanne in Switzerland. They employed a structure in which a dye formed from a ruthenium complex was fixed at the surface of a porous titanium oxide thin film, and realized a conversion efficiency that was comparable to that of amorphous silicon. Thus, the dye-sensitized solar cells instantly attracted the attention of researchers all over the world.
Hetherto, as metal complex dyes to be used in photoelectric conversion elements, N3, N719, Z907, and J2 have been developed. However, it was often the case that conventional dye-sensitized solar cells generally were low in photoelectric conversion efficiency and poor in durability.
Recently, as a metal complex dye which is excellent in terms of absorption coefficient in the wavelength range of 450 to 550 nm, photoelectric conversion efficiency, and stability, ruthenium metal complex dyes having terpyridyl and 3-trifluoromethyl-5-[4-(p-substituted phenylethenyl)-2-pyridyl]pyrazole, as ligands, were developed (see Non-Patent Literature 1). More recently in particular, solar sells get attention to and raise expectation for energy sources in place of nuclear power generation, and more improvement in performance of the solar sell has been required.